In an information processing system that includes a plurality of information processing apparatuses such as servers, power consumption values are managed for each information processing apparatus or each rack in which information processing apparatuses are mounted, to keep the total power consumption value of the information processing apparatuses from exceeding a limit. For example, each of a plurality of servers calculates the total power consumption value of the plurality of servers on the basis of information about power consumption values transferred among the servers, and when the total power consumption value exceeds a threshold, switches to an operation state in which power consumption is suppressed. In another example, when assigning virtual machines to a plurality of servers, a control apparatus controls the assignment of the virtual machines to the servers in accordance with a solution to an integer linear programming problem that minimizes a power consumption value for each rack in which servers are mounted. In some data centers, a power consumption value is calculated for each rack in which a plurality of information technology (IT) devices are mounted. When the calculated power consumption value exceeds a supposed value by a predetermined threshold or more, an alarm is output.
Related techniques are disclosed in, for example, Japanese Laid-open Patent Publication No. 2012-165549, International Publication Pamphlet No. WO 2013/042615, and Japanese Laid-open Patent Publication No. 2013-175120.
To keep a power consumption value from exceeding a limit value for a rack in which servers are mounted, the number of servers to be mounted in the rack is determined by, for example, multiplying the maximum value of electric power supplied to the rack by a safety factor and then dividing the resulting product by the power consumption value of a server operating at an operation rate of 100%. Although it is less likely that all servers placed in an information processing system of a data center operate at an operation rate of 100%, the number of servers to be mounted in a rack is set with a margin so that the information processing system is safely operated. For example, assuming that the rated value of electric power supplied to a rack is 4.8 kW, the safety factor is 85%, and the power consumption value of a server operating at an operation rate of 100% is 340 W, the number of servers to be mounted in the rack is set to “12”. If the average operation rate of servers during the operation of an information processing system is 70%, then the total power consumption value (2.86 kW) of the servers mounted in the rack is 60% of the rated value of electric power supplied to the rack. In this case, about 2 kW of 4.8 kW that may be supplied to the rack is not consumed and does not make a contribution to improvement of the performance of the information processing system.